<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>两栏布局</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        html,body{
            height: 100%;          
        }
        .box1{
            height: 100%;
            width: 200px;
            background: red;
            float: left;
        }
        .box2{
            width: calc(100% - 200px);
            height: 100%;
            background: yellow; 
            float: left;
        }
    </style>
</head>
<body>
    <div class="box1"></div>
    <div class="box2"></div>
</body>
</html>